Apparatus for and method of pulse keying



I. WOLFF APPARATUS FOR AND METHOD OF PULSE KEYING July 9, 1946.

Filed Dec 50, 1937 grllllllll a Lox s n 0 {noun Patented I July 1946APPARATUS FOR AND KEYING METHOD OF PULSE Irving Wolff, Merchantville,J., assignor to Radio Corporation of America, a corporation of DelawareApplication December 30, 1937, Serial N0. 182,418

11 Claims. (c1.25017) My invention relates to an apparatus for and amethod of pulse keyingand more specifically to a keying system in whichthe marking pulses are of extremely short duration.

- I am aware that numerous high speed mechanical keying systems havebeen devised for forming telegraphic characters. It has also beenproposed to use multivibrators for generating a keying pulse, Themultivibrator is used to establish currents of saw-tooth wave form.These currents are applied to a limiter which selects the peaks andthereby establishes a short marking impulse. In systems in which smallkeying powers are required, the multivibrator type keying may sufiice.When larger powers and extremely short marking pulses are required, theproblem is not as easily solved. For example, in systems which requiremarking pulses of the order of a microsecond or..less duration andsubstantial amounts of power, it becomes increasingly diflicult toshorten thepulses and equally difficult to efficiently amplify thepulses. 1

I propose to apply the initial pulses-to a device which not'onlyeificiently amplifies the pulses but also shortens the duration of thepulse. The device in certain respects resembles a resistance coupledamplifier in which inductors are substituted for the resistances, and inwhich only the positive pulses are transmitted. Keying or markingdevices of this type are used to start and stop oscillators, amplifiers,or modulators. In practice, myinvention may be applied to obstacledetectors operating on the radio echo principle, radio operatedaltimeters, television synchronizing impulses and the like. I

One of the objects of my invention is to provide means for generatingkeying pulses of very short duration and substantial amplitude.

Another object is to provide means for eniciently amplifying pulsecurrents having a, duration of the order of microseconds.

An additional object is to provide means for amplifying pulse currentsof short duration and simultaneously decreasing the pulse duration.

A still further object is to provide means for keying an obstacledetector transmitter by marking pulses of extremely high periodicity.

My invention may be best understood by reference to the accompanyingdrawing which is a schematic diagram. A multivibrator I,' whichgenerates currents of saw-tooth wave form 3, is connected through atransformer 5 to a vacuum tube amplifier l. Theprimary 9 of thtransformer 5 may be shielded from thesecondary ll.

byan electrostatic screen I3. The secondary. II is preferablyof lowimpedance and, together'with the'input capacity of the amplifier I, maybe arranged to resonate at substantially the period of the applied pulseI5. The grid electrode I4 of the .2 amplifier l is. biasedLne'gativelywith respect to cathode I6 bya biasing battery l1.

The anode. of the amplifier I is connected through a low impedanceinductor I9 to the positive terminal of a B battery 2|. The negativeterminal of the battery 2| isconnected to the positive terminal of thebiasing battery I'I, cathode I6, and ground. The inductor I9 is coupledthrough a blocking capacitor 23 to the grid 24 of a second amplifier 25.,The grid Ziisbiased negatively with respect to. cathode 26 by a gridresistor 21 which is connected to the' negative terminal of the biasingbattery 25. The natural period of the inductor 25 andassociatedcapacities is preferably of the order of the natural period ofthe applied pulses 29.

The anode of amplifier 25 is connected through a low. impedance inductor3| to the positive terminal of the B battery 2!. A potentiometer 33 isshunted. across the inductor 3|. The inductor is coupled through anetwork 35 and a serially connected source 31 of biasing voltage to keyan oscillator 39 or the like. The output of the oscillator is applied toan antenna 4| or otherload circuit.

Having described the circuit, the mode of operation will be set forth;In the condenser char ing circuit of the multivibrator, pulses ofcurrent are available. These discrete pulses l5 are applied to theprimary 90f the transformer 5. The pulses l5 are suitably phased by thetransformer II so that the grid I4 is driven positive with respect toits cathode I6. p 1

r The amplified positive pulses act on the in ductor I9 and, due to itsdifferentiating effect in a mathematical sense, create negative pulsesduring the rise and positive pulses during the fall of current of pulsesI8. Due to the action of the resonant circuit, including inductor l9 anditsassociated capacities in tubes 1 and 25, and the shunt resistor 21and grid circuit losses in tube 25; a highly damped wave train- 29 iscreated. It will be observed that the duration of the first negative andfirst positive portions oi the wave train 29 is substantially equal tothe duration of the applied-positive pulse, Thus the original pulseduration is decreased.

The wave train 29 is applied through the blocking capacitor 23 to theinput of the second amplifier 25. This amplifier is biased so that itsoutput current is near cut-01f. Because of this bias, the first positivepulse of the wave train '29, and sometimes the following positive pulse,will actuate the amplifier 25. The inwill overcome the bias 3'! whichnormally prevents the oscillator 39 from functioning and will abruptlykey the oscillator. The oscillator 89, thus keyed, will generateoscillatory currents 34 during a portion of the first positive pulseduration. The pulse duration may be adjusted from a fraction of amicrosecond to several microseconds. other at the required rate ofkeying. 4

It should be understood that the transformer 5 may be replaced by aninductor, blocking capacitor and grid resistor. In order to effectivelymatch impedances, the inductors may be used as autotransformers.

I claim as my invention:

1. A pulse generator device including in combination a source of rapidlyvarying currents, means for transforming said currents into highlydamped wave trains, means for amplifying the positive pulses of saidwave trains, and means for applying the amplified positive pulses to anoutput circuit.

2. A pulse keying device for a transmitter including in combination asource of pulses, means for transforming said pulses into highly dampedwave trains, means for amplifying the first positive pulse of said wavetrain, means actuated by said amplified positive pulse for creating asecond highly damped wave train, and means for applying the firstpositive pulse of said second highly damped wave train to key saidtransmitter.

3. A keying device including in combination a circuit to be keyed, asource of discrete pulses, means for converting said discrete pulsesinto a a first series of highly damped wave trains, means for amplifyingthe first positive pulse of said wave trains, means for deriving fromsaid amplified positive pulses a second series of highly fortransforming said pulses into series of wavetrains, means for highlydamping said Wave trains, said trains including negative phased pulsesand positive phased pulses, means for amplifying the first of each ofsaid positive pulses, means responsive to said positive pulses forcreating a second series of wave trains, means-for highly damping saidsecond series of Wave trains, said second series of wave trainsincluding negatively phased pulses and positive phased pulses and meansfor applying the first of each of said last-mentioned positively phasedpulses to a keying circuit.

5. The method of establishing and applying keying pulses to a loadcircuit which comprises, generating discrete discharge currents,converting said discrete discharge currents into discrete pulses,transforming said discrete pulses into wave trains including highlydamped negatively and positively phased pulses, amplifying saidpositively phased pulses, and applying the first of said amplifiedpositive pulses to said load circuit.

6. The method of establishing keying pulses of extremely short durationwhich comprises generating discrete discharge currents, converting saiddiscrete discharge currents into discrete pulses, transforming saiddiscrete pulses into v highly damped oscillatory currents, amplifyingThe keying pulses may follow each he first positively phasedoscillation, converting said amplified oscillation into a second seriesof highly damped oscillatory currents, and deriving from said lastoscillatory currents a positively phased pulse of extremely shortduration.

'7. A pulse keying device including a source of discrete pulses ofcurrent of a single phase, means for converting each of said pulses ofsingle phase into currents of positive and negative phases forminghighly damped wave trains,

means for selectively amplifying currents of the first positive phase ofeacli of said wave trains, and means for creating from said positivephase currents a second current having negative and positive phases ofless duration than said first mentioned currents of positive andnegative phases.

8. A pulse keying device including a source of discrete pulses ofcurrent of a single phase, means for converting each of said pulses ofsingle phase into highly damped waves including currents of positive andnegative phases, means for selectively amplifying currents of the firstpositive phase of each of said waves, and means for creating from saidpositive phase currents a second current having negative and positivephases of greater amplitude and less duration than said first mentionedcurrents of positive and negative phases.

9. A pulse keying device including a source of discrete pulses ofcurrent of substantially uniform duration, means for converting saiddiscrete pulses of currents into highly damped waves includingpositively and negatively phased currents, the period of said two phasesbeing 01' substantially the same duration as said discrete pulses, andmeans for selecting in each of said Waves the first positive phasecurrents and excluding said negatively phased currents whereby theduration of said selected phases is less than the duration of saiddiscrete pulses.

10. A pulse keying device including a source of discrete pulses ofcurrent of substantially uniform duration, means for converting saiddiscrete pulses of currents into highly damped Wave trains includingpositively and negatively phased currents, the period of said two phasesbeing of substantially the same duration as said discrete pulses, meansfor selecting the first of the positively phased currents of each ofsaid Wave trains and excluding said negatively phased currents wherebythe duration of said selected phases is less than the duration of saiddiscrete pulses, means for amplifying said positively phased currents,and means for establishing currents of positive and negative phases of aduration controlled at least in part by said first mentioned positivelyphased currents.

11. A pulse amplifier including a source of positive pulse voltages,means for converting said positive pulse voltages into a highly dampedwave train having negative and positive voltage peaks,

4 and means for amplfying the first positive peak without amplifyingnegative peaks of said wave train.

IRVING WOLFF.

